Two-step ammunition feeder

ABSTRACT

An automatic gun is provided with a reciprocating bolt carrier having cam surfaces extending along its exterior for reciprocating a follower which operates an ammunition feed mechanism. A lower cam surface is formed directly on the bolt carrier and an upper cam surface is formed on the upper surface of an elongated ramp pivotally mounted on the bolt carrier. The ramp is movable between two positions to cause the follower to follow the lower cam surface when the bolt carrier moves forwardly and to follow the upper cam surface when the carrier reverses. The slope of the cam surfaces is such that the follower moves through its total downward return stroke when engaging the forward portion of the lower cam surface and then is gradually advanced upwardly during the remainder of its contact with the lower cam surface and throughout its entire contact with the upper cam surface.

United States Patent lnventor Eugene M. Stoner Primary ExaminerSamuel Feinberg 2292 No. Carriage Lane, Port Clinton, Assistant Examiner-Stephen C. Bentley Ohio 43452 Attorney-Fowler, Knobbe & Martens Appl. No. 855,492 Filed Sept. 5, 1969 patented 28 197 ABSTRACT: An automatic gun is provided with a reciprocating bolt carrier having cam surfaces extending along its exterior for reciprocating a follower which operates an ammunition TWO-STEP AMMUNITION FEEDER feed mechanism. A lower cam surface is formed directly on 9Claims, 35 Drawing Figs. the bolt carrier and an upper cam surface is formed on the upper surface of an elongated ramp pivotally mounted on the bolt carrier, The ramp is movable between two positions to cause the follower to follow the lower cam surface when the n n bolt carrier moves forwardly and to follow the upper cam sur- A 33 B 33 BB 33 C 45 face when the carrier reverses. The slope of the cam surfaces is such that the follower moves through its total downward return stroke when engaging the forward portion of the lower {56] References Cited UNITED STATES PATENTS l0/l904 Dawson et al. 9/ l 940 Conlon 89/33 C X 89/33 BB UX PATENTED DEC28 I97| sum 02 or 2 m s N mmw .MQEA

PATENTEDDEE28197I SHEET 03 0F PATENTED M828 15m SHEET 0 7 UP INVENTOR. EUGENE M STONE? 3 M w 6 m w a kw 5H J MM PATENTED H6228 Em SHEET IOUF 12 INVENTOR. U6N M STONE/Q BY F0144 5e, A/NOBBE ATTOFN SYSZ PATENTED [15828 1971 SHEET llflF 12 INVENTOR. 5065M. M 570N616 TWO-STEP AMMUNITION FEEDER RELATED APPLICATION This application discloses an automatic gun which is similar to that set forth in a patent application entitled Automatic Gun by Eugene M. Stoner filed Sept. 29, I965, Ser. No. 49l,300, issued as US. Pat. No. 3,455,204 on July I5, 1969, with the exception that the instant application employs a different arrangement for operating the ammunition feed mechanism.

BACKGROUND OF THE INVENTION This invention relates to automatic guns, and particularly to rapid firing, short recoil operated automatic guns.

In rapid firing automatic guns, one of the limiting aspects of the speed attainable is the speed at which the ammunition can be fed into the gun. In the high-speed automatic weapon described in the above-referenced patent application, a bolt carrier is axially reciprocated past an ammunition feeding station, and a cam track or surface in the side of the bolt carrier receives a follower connected to drive an ammunition feed mechanism. As the bolt carrier moves rearwardly through one stroke of its cycle, the follower is raised through its upward stroke, thus lifting the ammunition belt to feed the next round of ammunition. As the carrier moves forwardly completing the other stroke of its cycle, the follower rides on the same cam surface through its downward stroke into position for feeding the next round of ammunition.

While the foregoing arrangement works very well, the operation could be improved. As higher speeds are attempted, a limiting factor becomes the acceleration which can be applied to an ammunition belt. With increased acceleration there is some danger of the belt of ammunition becoming separated in view of the short period of time in which sufficient force must be applied to raise the belt of ammunition one round. The gun described in the above-referenced pending patent application was designed to fire 25 mm. shells at approximately 700 rounds per minute. Thus, the bolt carrier completes its two-stroke cycle 700 times per minute, which in turn means that the strokes of the bolt carrier occur at the rate of 1,400 per minute, which allows about 40 milliseconds per stroke. Thus it can be appreciated that the force required to raise the belt of ammunition one round in such a short interval is very substantial; and as pointed out above, increasing the speed of operation increases these forces and thus the possibility of the belt separating. Hence, it is desirable that the ammunition feeding process be modified in a manner to allow more time in which to raise the belt of ammunition for a given feed cycle rate. This in turn permits greater overall cycle speed for the bolt carrier to enable automatic guns to be fired at even more rapid rates than the 700 rounds per minute mentioned above.

SUMMARY OF THE INVENTION In accordance with this invention, a reciprocating bolt carrier is provided with a novel cam means by which a cam follower connected to an ammunition feed mechanism is lowered at a speed much faster than that at which the follower is raised. The follower can be lowered in a very short time interval in that the belt of ammunition is not moved while the follower is being lowered and hence there is essentially only the light weight of the follower itself being moved, and gravity is assisting this. To attain high speed, the follower is lowered during only a portion of the forward stroke of the bolt carrier cycle. The remainder of that forward stroke of the bolt carrier is utilized to start raising the belt of ammunition one round, and the rearward stroke of the bolt carrier is then used to continue the raising of the belt of ammunition that one round. The result of this is that the majority of the bolt carrier cycle can be utilized in raising the belt of ammunition one round whereas in the arrangement described in the above-referenced copending application, one one-half of the cycle is utilized for raising a round of ammunition. Consequently, ifthe same time interval is used for raising the belt of ammunition one round in each arrangement, a much faster overall feed cycle, and hence firing rate, can be attained with the novel cam means described herein.

In a preferred arrangement, this novel cam means includes a fixed lower cam surface, a forward cam surface forming an extension of the lower cam surface, and a rear cam surface forming a rear extension of the lower cam surface. The cam means further includes a ramp which is pivotally mounted on the bolt carrier adjacent the lower cam surface and with the ends of the ramp terminating adjacent the front and rear cam surfaces. The upper surface of the ramp forms an upper cam surface for the cam follower. The ramp is pivotable between two positions in a manner to direct the cam follower to ride on the cam surface in the proper sequence.

In a first position, the forward end of the ramp is spaced from the forward cam surface by an amount sufficient to permit the cam follower to move from the forward cam surface onto the lower cam surface. The rear of the ramp, while in the first position, engages the lower cam surface so that the upper cam surface on the ramp forms a continuation of the rear cam surface. In the second position of the ramp, the arrangement is reversed such that the forward end of the ramp engages the forward portion of the lower cam surface so that the upper cam surface on the ramp forms an extension of the forward cam surface and the rear end of the ramp is spaced from the lower cam surface an amount sufficient to enable the follower to move from the lower cam surface onto the rear cam surface. Biasing means are provided urging the ramp into its first position. However, the strength of this biasing means is such that it can be easily overcome by the follower as the follower is driven by the bolt carrier.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view showing the exterior of a gun constructed in accordance with this invention;

FIG. 2 is an enlarged sectional view taken generally along lines 2-2 of FIG. 1;

FIGS. 3a and 3b are fragmentary, enlarged side views, in section, showing portions of the recoil assembly illustrated in FIG. 2;

FIG. 4 is a sectional view taken generally along lines 4-4 of FIG. 3a;

FIG. 5 is a perspective view showing a part of the recoil assembly removed from the gun;

FIG. 6 is a sectional view taken generally along lines 6-6 of FIG. 2;

FIGS. 7-9 are fragmentary, enlarged side views, in section, showing he central portion of the gun illustrated in FIG. 1 in successive stages of the firing cycle;

FIG. 10 is an enlarged sectional view taken generally along lines 10-10 of FIG. 2;

FIG. 11 is an enlarged sectional view taken generally along lines ll-Il of FIG. 2;

FIG. 12 is an enlarged sectional view taken generally along lines 12-12 of FIG. 2;

FIGS. 13-16 are fragmentary, enlarged side views, in section, showing the rear portion of the gun illustrated in FIG. 1 in successive stages of the firing cycle;

FIG. 17 is an enlarged, rear elevation view of the gun illustrated in FIG. 1 with portions cut away;

FIG. 18 is a sectional view taken generally along lines 18- 18 of FIG. 15;

FIG. 19 is a perspective view of the rear buffer and rear assembly removed from the gun;

FIGS. 20 and 21 are fragmentary, enlarged top views, in section, showing the central portion of the gun illustrated in FIG. I, and particularly illustrating the ammunition feeding means in successive stages of the firing cycle;

FIG. 22 is a sectional view taken generally along lines 22- 22 of FIG. 20;

FIG. 23 is a sectional view taken along the same lines as FIG. 22, but showing the bolt and bolt carrier in the forward position;

FIG. 24 is a perspective view of a portion of an ammunition belt removed from the gun;

FIG. 25 is a fragmentary, perspective view of the ammunition feeding means with portions cut away;

FIG. 26 is a perspective view ofa portion of the ammunition feeding means removed from the gun;

FIG. 27 is a fragmentary perspective view, in vertical, longitudinal section, showing the central portion of the gun in the counter-recoil part of the cycle;

FIG. 28 is an exploded perspective view of the bolt carrier and the cam means for operating the ammunition feed mechanism;

FIGS. 29-33 are schematic views illustrating the bolt carrier in various stages of longitudinal reciprocation and the cam follower for the feed mechanism in the corresponding stages of the vertical reciprocation; and

FIG. 34 is a diagram of a circuit for selecting a fully automatic or semiautomatic firing cycle responsive to the ammunition feed selector.

Referring to FIGS. 1, 2 and 6, an automatic gun is shown, including a barrel 5, and receiver 6, and ammunition feeding means 7. The gun is mounted, e.g. on a vehicle such as a military armored car, by an exemplary means which includes a collar 11 having internal rails 12 which fit into conforming external grooves 13 on the side of the receiver. A removable pin 14 extends through aligned apertures l5, 16 in the collar and receiver 6 to fix the gun longitudinally with respect to the collar. The collar 11 is supported on a horizontal pivot pin 18 in a yoke 17. A vertical pin 19 extends from the base of the yoke for mounting the same on a vehicle (not shown) for pivotal movement about a vertical axis. Thus, the gun is positively fixed against sliding movement relative to the vehicle, but may be pivoted to aim the gun.

The barrel is mounted for reciprocal movement along the axis 26 of its bore in the forward portion of an elongate, generally cylindrical, upper part 25 of the receiver. A bolt means or carrier mechanism is provided for chambering, firing and ejecting rounds of ammunition 27. The bolt means includes a bolt 28, which is aligned with the barrel axis, and a bolt carrier 29 which is attached to the bolt and reciprocates longitudinally in the receiver past an ammunition feeding station 30 located rearward of the barrel. The bolt carrier 29 has a relatively short upper sleeve portion 3! which carries the bolt, and a relative long, lower body portion 32 which is housed in a lower, generally rectangular, part 33 of the receiver.

A recoil assembly 36 located beneath the barrel is operably coupled between the barrel and the forward end of the receiver lower part 33 for buffering recoil and counterrecoil forces. The recoil assembly is aligned with the body 32 of the bolt carrier and engages its forward end to accelerate the bolt carrier 29 in recoil relative to the barrel.

The recoil force of the bolt 28 and carrier 29 is buffered by a buffer assembly 38 at the rear of the receiver which engages the rear of the bolt carrier sleeve 31 near the end of the recoil stroke. A sear 41 pivotally connected to the buffer assembly 38 engages in a scar notch 42 on the bolt carrier body 32 to interrupt counter-recoil movement of the bolt and bolt carrier and retain them in the rearward cocked position. Depression of a trigger mechanism 40 raises the sear 41 out of engagement with the notch 42 to fire the gun.

A muzzle brake 43 is connected on the forward end of the barrel to permit gas to escape rearwardly through openings in the brake.

Referring now to FIGS. 6 and 9, as well as to FIG, 2, a breech barrel extension 48 is threaded onto the rear of the main barrel portion. The external surface of the barrel extension forms a bearing surface which slideably engages an internal bearing surface 49 in the upper forward portion 25 of the receiver. A collar 50 affixed around the barrel also has an external bearing surface 51 which slideably engages a corresponding internal bearing surface 52 in the forward end of the upper forward receiver portion 25 to support the barrel. A shoulder 53 at the forward end of the barrel collar 50 abuts a shoulder 54 intermediate the ends of the barrel, and a nut 55 threaded onto the barrel forward of the collar holds the collar in place longitudinally. Tabs 56 on a lock washer 57 between the nut 55 and the collar 50 are bent in opposite directions into detents on the collar and nut to retain the nut 55 against accidental loosening. The collar is fixed against rotation relative to the barrel by an internal longitudinal key 60 on the collar which is inserted in a corresponding keyway 61 formed in the barrel. A lug 62 which depends downwardly from the collar, extends through a forwardly open guide slot 63 in the receiver, and engages the sides of the guide slot to fix the collar 50 and barrel against rotation relative to the receiver, while permitting axial reciprocation.

Referring particularly to FIGS. 2, 3a and 3b, the recoil assembly 36 includes a recoil cylinder 70 to the forward end of which extends through an ear 7] depending from the receiver 6 and the rear end 72 of which is threaded into the front of the receiver lower part 33, so that the cylinder extends parallel to and below the barrel axis 26 in alignment with the bolt carrier body 32. The recoil cylinder 70 houses a recoil piston 73 which has a piston head 75 and a piston rod 74 extending forward from the head and on through an aperture 76 in the depending portion of the barrel collar lug 62. A sleeve nut 77, threaded onto the piston rod 74 has an external flange 78 which abuts the barrel collar lug 62 to retain it on the piston rod. Accidental loosening of the sleeve nut 77 is prevented by a spring-biased plunger 79 which engages in any of a plurality of detents 80 formed around the flange 78 of the nut. An adjusting nut 83 on the piston rod rearward of the collar lug 62 accurately locates the longitudinal position of the barrel relative to the receiver and recoil mechanism. An arcuate piece of resilient material 85 is wedged into a tapered arcuate slot 86 in the adjusting nut to hold it at any selected place of adjustment along the threads 87 of the piston rod.

The sleeve nut is knurled on its external surface so as to facilitate its removal by hand. With the sleeve nut 77 removed, the barrel may be freely slid out the forward end of the receiver.

Because the recoil piston rod 74 is fixed to the barrel 5 by the sleeve nut 77 and adjusting nut 83, the recoil piston head 75 reciprocates rearwardly and forwardly with the barrel in the recoil and counter-recoil, respectively.

The recoil piston head reciprocates in a front bore 91 of relatively large internal diameter in the recoil cylinder 70, and an accelerator piston 93 reciprocates in a rear bore 92 of smaller internal diameter in the cylinder. The accelerator piston 93 includes a piston head 95 sealed by an O-ring seal 96. The interior of the recoil cylinder, between the recoil piston head 75 and the accelerator piston head 95, is filled with hydraulic fluid so that as the recoil piston moves rearwardly in recoil, the smaller diameter accelerator piston 93 is driven rearwardly at an increased velocity.

The accelerator piston 93 is hollow. It has a closed forward extension 101 protruding forward from the piston head 95 and also has an open rear extension 107 which protrudes rearwardly from the piston head 95. In recoil, the rear extension 107 of the accelerator piston engages the aligned forward end 97 of the bolt carrier body 32 to push the bolt carrier 29 rearward from the battery position illustrated in FIG. 2. Rearward movement of the accelerator piston is limited by an interior shoulder 108 at the rear end of the recoil cylinder.

A heavy recoil spring 98 interior of the recoil cylinder is compressed between a shoulder 99 in the cylinder wall and the recoil piston head to urge the recoil piston 73 forward. The accelerator piston 93 is urged forward by a lighter return spring 100, which is housed in the hollow accelerator piston and the closed forward extension 10] thereof nested within the recoil spring 98. The accelerator spring 100 is compressed between the closed forward end of the accelerator piston and a plug 102. The plug 102 is slideably mounted within the rear extension 107 of the accelerator piston and abuts a stop pin 103 which is fixed to the recoil cylinder 70 and extends through an elongate slot 104 in the rear extension of the accelerator piston. In its forward position, the accelerator piston head 95 abuts an annular ring 105 interposed between the shoulder 99 and the recoil spring 98. Since the recoil spring is considerably stronger than the accelerator spring, this limits forward movcment of the accelerator piston.

A wedge-shaped, or tapered, throttling groove 110 (FlGS. 3a and 4) is formed in the (FIGS. of the large diameter part of the recoil cylinder. The throttling groove 110 permits a programmed amount of fluid to bypass the recoil piston head after the recoil piston head has moved a selected distance rearward in recoil. An annular spacer 111 (FlGS. 3a and 5) having forwardly extending spaced-apart fingers 112 is interposed between the forward end of the recoil spring and the recoil piston head to provide radial passageways I13, assuring that fluid communication between the throttling groove 110 and the fluid in the chamber portion rearward of the piston head 75 is not blocked off by compression of the recoil spring 98. Sealing of the bypass 110 is a particular problem because the high acceleration encountered in rapid firing automatic guns causes the recoil spring to compress dynamically, with the greatest amount of compression in the forward portion adjacent the recoil piston head at the initial stages of recoil.

The chamber within the recoil cylinder 70 is sealed at the rear end by the accelerator piston head seal 96. At the forward end. the chamber is effectively terminated by a threaded plug 115 through which the recoil piston rod 74 extends in engagement with an O-ring seal 114. The recoil piston head 75 divides the chamber within the recoil cylinder into a rear chamber and a forward chamber. The recoil piston head is approximately the same diameter as is the forward bore 91, but there is no seal between the piston head and bore. Air may be bled from the cylinder chamber by backing off a setscrew 116 to unseat a ball valve 117 in the plug 115.

A bellows-type cover 118 extends between the plug 115 and the adjusting nut 83 to enclose the extended sealing surface of the recoil piston rod 74.

The recoil piston head 75 has a check valve 122 formed thereon to facilitate the return of the barrel to battery position in time to receive the next round. The check valve 122 opens on forward movement of the recoil piston to permit fluid to flow rearwardly through a plurality of small orifices 123 in the recoil piston head. The valve 122 includes an annular flapper ring 124 which is seated by a spring 125 compressed against an outwardly extending shoulder or cap 126 fixed on a central rear extension 128 on the recoil piston head, to seal the orifices 123 except during forward movement of the piston head.

Belville or cup counter-recoil springs 127 stacked in seriesparallel forward of the recoil piston head cooperate with the piston head and the plug 115 to buffer counter-recoil forces.

The recoil piston rod 74 is hollow to provide a reservoir for replenishing hydraulic fluid in the chamber of the recoil cylinder, and to accommodate thermal expansion of the fluid. A replenisher piston 130 is slideable in the reservoir chamber 131 and sealed by an O-ring 132 around the piston head 133. The replenisher piston is biased rearwardly by a replenisher spring 134 which surrounds the replenisher piston rod 135 and abuts a cap 136 retained in the forward end of the recoil piston rod 74.

If the volume of hydraulic fluid in the recoil cylinder decreases, either through temperature decrease or leakage, the differential pressure between the reservoir 131 and the main chamber 94 opens a spring-biased ball check valve 138 in the piston head to provide a conduit through which fluid may flow to replenish the supply in the recoil cylinder.

On the other hand, as the temperature of the hydraulic fluid in the recoil cylinder increases, the hydraulic fluid seeps forward around the recoil piston head, which is not sealed against the walls of the chamber. It passes through a small bleed hole 139 in the wall ofthe recoil piston rod and into the replenisher reservoir, thus forcing the replenisher piston forward against the replenisher spring. The replenisher spring 134 is considerably weaker than the accelerator spring 100, so that expansion of the hydraulic fluid will cause the replenisher piston, rather than the accelerator piston 93 to move.

if expansion of the fluid is great enough, the replenisher piston moves forward of a radial outlet 140 through the side of the recoil piston rod so that fluid seeps out between the threads of the adjusting nut 83 and the recoil piston rod. The external surface 141 of the recoil cylinder is circumferentially rigid to provide an increased cooling surface, and decrease the likelihood of overexpansion.

Because the bleed hole 139 is quite small and the recoil cycle time is extremely short, the replenisher piston does not move substantially under the influence of the instantaneous pressure increase in the main fluid chamber 94 caused by recoil of the recoil piston.

The distance which the replenisher piston rod 135 extends forward out of the recoil piston rod 74 is proportional to the quantity of hydraulic fluid in the recoil cylinder; hence, the replenisher piston rod serves as a dipstick to indicate the supply of fluid by index marks (not shown) on the dipstick which are visible through an aperture 142 in the sleeve nut 77.

Referring particularly to FlGS. 10-12 and 27, as well as FIG. 2, as the bolt carrier 29 reciprocates, two laterally spaced legs 148 on the forward end of the bolt carrier body 32, and two laterally spaced legs 149 on the rear of the body 32 are guided in longitudinal trackways 150 formed in the bottom plate 151 of the receiver 6. Raised bearing surfaces 152, 153 and 154 located on the upper side of the body 32 at the forward end, the center 153, and the rear end 154 thereof respectively, slidingly engage the bottom surface of parallel elongate guide rails 155 which are mounted interior of the sides of the receiver. The sides of a neck portion 156 of the bolt carrier, which integrally connects the upper sleeve portion 31 to the lower body portion 32, bear against the sides of these rails 155 to fix the top of the bolt carrier laterally with respect to the receiver. Thus, as the bolt carrier reciprocates longitudinally in the receiver, the guides maintain the bolt in axial alignment with the barrel.

Referring particularly to FIGS. 7, l0 and 27, external locking lugs or teeth 160 at the forward end of the bolt engage with internal locking lugs or teeth 161 at the rear end of the barrel extension to lock the bolt to the barrel when the bolt is in battery. When the bolt is rotated from the locking position to a position in which the teeth 160 on the bolt are aligned with the spaces between the teeth 161 on the barrel extension, the bolt is unlocked and may be reciprocated rearwardly away from the barrel.

Referring now particularly to FIGS. 7, 11 nd 27, the bolt 28 is inserted in the sleeve portion 31 of the bolt carrier for axial and rotative movement, and connected to the sleeve by a cam follower pin 162 extending through the bolt and into radial surface cam slots 163 on opposite sides of the bolt carrier sleeve. The cam pin is held in place by the interior walls of the receiver 6. The forward and rearward portions of the cam slots are parallel to the barrel axis to permit limited axial movement of the bolt in the carrier sleeve-with the bolt in the aligned position when the cam follower pin 162 is in the forward portion of the slots and in the locked position when the cam follower pin is in the rear position. The central portion of the cam slot is oblique to the bolt axis to rotate the bolt between the locking position and the aligned position. Thus, as the bolt carrier body is accelerated rearwardly relative to the barrel by the recoil mechanism 36, the cam follower pin cooperates with the cam slot to rotate the bolt to the aligned position, and then carry the bolt rearward with the bolt carrier.

When the bolt leaves the barrel it is in the aligned position, and is extended forward in the sleeve. As is shown in FIGS. 7, l3 and 18, a spring-biased crevice pin 165, mounted in the bolt carrier neck and sleeve for radial movement with respect to the barrel axis, is urged upward into a notch 166 in the bolt to hold the bolt forward in the sleeve, and therefore in the aligned position. A cam follower or ramping pin 167 extends outwardly from the crevice pin 165 and rides on elongate cam surfaces formed on the top of the guide rails 155 to hold the crevice pin in the upward, engaged position after the bolt is out of battery so that the bolt remains extended despite forces on it from stopping the bolt carrier at the rear of the receiver and from stripping rounds during the counter-recoil stroke. The forward edge of the crevice pin 165 is beveled so that the bolt forces the crevice pin out of engagement when the bolt returns to battery and strikes the barrel, while the sleeve 31 is still moving forward in counter-recoil.

An extractor claw 168 extends forward of the bolt to grip the lip 169 of a cartridge case. The claw 168 is connected to the bolt by a pivot pin I70 and urged into the gripping position by a spring 171. A beveled surface 172 on the leading edge of the claw causes it to ride up over the lip of a cartridge as the bolt moves forward to engage a cartridge. A firing pin 173 is affixed to the rear end of the bolt carrier sleeve by a pin 178 held in place by the walls of the receiver 6. The firing pin 173 extends slideably through a bore 174 in the bolt. A cartridge ejecting rod or pin 175 also extends slideably though a bore pin 176 in the bolt and an arcuate aperture 177 (see FIG. 12) in the rear end of the bolt carrier sleeve. The ejecting pin 175 is caught between the bolt and carrier sleeve by an enlarged shoulder 180 formed intermediate its ends and accommodated by aligned recesses in the bolt and sleeve.

Referring particularly to FIGS. and 19 the buffer assembly 38 at the rear of the receiver includes a plurality of annular cup or Belville springs 182 stacked in series and aligned with the bolt carrier sleeve 31. The Belville springs 182 are housed in a cylindrical sleeve 183 mounted for longitudinal sliding movement at the rear of the receiver. The sleeve has an integral rear end plate 184 which abuts the backplate 185 of the receiver. A plunger 186 is longitudinally slideable in the forward end of the sleeve and is held against the Belville springs by a stop or screw 187 slideably extending through the plunger 186 and end plate 184 and threaded into the back plate 185 of the receiver. The screw may be tightened or loosened, as desired, to adjust the preloading of the Belville springs 182.

As the bolt carrier nears the end of its recoil stroke, the rear face 190 of the bolt carrier sleeve engages the plunger 186 and compresses the Belville springs 182 rearwardly against the end plate 184 of the buffer sleeve to gradually stop the recoiling bolt and bolt carrier. The Belville springs then expand and shoot the bolt and bolt carrier forward toward the battery position for firing another round.

The sear 41 is pivotally mounted on the lower side of the buffer sleeve intermediate the ends of the sleeve by a pin 192 extending through apertures in a pair of lugs 193 affixed to the sleeve. A compression spring 194 engaged between sleeve 183 and the sear urges the sear downward into engagement with the sear notch 42 formed in the upper surface of the bolt carrier body 32 near the rear end of the body.

The trigger 40 is mounted on the rear plate 185 of the receiver by a pivot pin 195. The trigger has a forward portion 44 which extends into a notch 45 formed in the rear end of the carrier body 32 (FIG. 27) so that the forward portion of the trigger underlies the sear. The trigger may be activated manually or by a solenoid 196 to hold the sear up out of engagement with the sear notch so that the bolt carrier will return to the battery position. If the trigger is released, the spring 194 urges the sear downward to engage in the sear notch and interrupt the counter-recoil stroke of the bolt carrier, thereby holding the bolt carrier in the rearward cocked position. The sear force is buffered by the sleeve 183 compressing the Belville springs 182 forward against the screwhead 188 and plunger 186 as the sleeve 183 slides forward in the receiver (FIG. 16).

Referring particularly to FIGS. 7, 9 and 13, a long operating spring 200 extends through an opening 201 in the bolt carrier body 32 and is compressed between the backplate 185 of the receiver and the forward part of the bolt carrier body 32 to drive the bolt carrier forward. The operating spring 200 is guided on a rod 202 which is affixed to the backplate of the receiver by a pin 203 and extends slideably through a bore 204 in the front end of the carrier body 32. A keeper 233 is slideable on the rod 202 and is retained by an enlarged head 234 on the forward end of the rod. The forward end of the guide rod 202 extends into the open rear end 107 of the accelerator piston 93 to support the rod when the bolt carrier is rearward from the battery position.

A charging system is provided for pulling the bolt carrier from the battery position rearward to the cocked position. As seen in FIGS. 1, 2 and 7 through 12, the charging system includes a chain 205 which is nested between the pairs of bolt carrier legs 148, I49 and extends along the receiver through a central way 206 formed in the bottom plate 151 of the receiver 6. The forward end of the chain is connected to a charging block 207 which freely engages the forward end of the bolt carrier body 32 as the chain is pulled rearwardly. The block 207 travels along the way 206 on a guide rod 208 which extends through an aperture 209 in the block into an aperture 210 at the forward end of the receiver. The rear end of the charger guide rod is affixed to the receiver by a support 211 extending up from the bottom plate. The chain is engaged by a sprocket 215 journaled on the bottom plate at the rear of the receiver. The sprocket may be rotated by a removable manual crank 216 (see FIGS. 1 and 17), or by a powered means (not shown). An elongate spring 220 is guided on the rod 208 and returns the block 207 to the forward position.

Referring to FIGS. 13 and 17, the backplate of the receiver is connected to the receiver by upper and lower removable pins 217 extending through ears 218 on the receiver and brackets 214 on the backplate. With the pins 217 removed, the backplate may be removed from the receiver along with the trigger 40, the solenoid 196, the buffer 38, sear 41 and the bolt carrier operating spring 200 and guide rod 202, all of which are attached to the backplate. The bolt 28 and bolt carrier 29 are then free to be pulled out the rear of the receiver whereupon the various points 162, 178 are no longer retained by the surfaces of the receiver and the bolt is easily removed from the carrier and disassembled.

As is shown most clearly in FIGS. 1, 11, 20-23, 25 and 27, the ammunition feeding means 7 includes similar rightand left-hand ammunition guides or feeding trays 228, 229 disposed on opposite sides of the receiver 6 at the feeding station 30. Each of the feeding trays 228, 229 guides rounds 27, 27a, 27b, etc. of ammunition from a different store to the feeding station 30.

The two ammunition feeding trays 228, 229 are pivotally attached to the receiver by a pair of vertical mounting rods 219 forward of the tray, each extending through upper and lower ears 221 on the trays and upper and lower brackets 223 on the receiver. As seen in FIGS. 11, typically each mounting rod 219 has an upper portion 222 spring loaded in telescoping relationship with a lower sleeve portion 224. The two feeding trays are interconnected or ganged at their rear ends by upper and lower horizontal connecting bars 225, 226 which slide through corresponding keyways 227 transverse to the receiver as the trays pivot about the forward mounting rods 219. The connecting bars 225, 226 are connected to the trays by vertical rear mounting rods 230 which are similar to the front mounting rods 219 and which extend through aligned apertures in the bars and in upper and lower brackets 232, 235 extending rearwardly from the respective trays. Each of the feeding trays can be removed from the receiver by telescoping the mounting rods 219, 230 to remove them from the respective brackets.

In FIGS. 20-23, 25 and 27 the right-hand tray 228 is shown in the operative or feeding position adjacent the receiver, and the left-hand tray 229 is pivoted away from the receiver to the disengaged position. A selector is provided for pivoting one or the other of the ganged ammunition feeding trays to the operating position to select feed from either of the ammunition stores. The selector includes a selector handle 236 pivotally connected by a telescoping mounting rod 237 to brackets 238, 239 fixed on the receiver rearward of the righthand tray. The selector handle 236 is operatively connected to the right rear tray-mounting rod 230 by upper and lower angle selector levers 240, 241 which pivot with the selector handle 236 about the selector mounting rod 237. ONe end of each lever 240, 241 is affixed to the selector handle 236, and the other end has a forward opening slot 242 which receives the end of the right rear ammunition tray mounting rod 230. As the selector handle is pivoted rearwardly about the selector mounting rod 237, the angle levers 240, 241 cause the ammunition feeding tray connector bars 225, 226 to move to the right, thus pivoting the right-hand ammunition feeding tray laterally out of the operable position and the left-hand ammunition feeding tray laterally into the operable position, as is shown in phantom in FIG. 20.

A trigger-type latch 245 (see also FIG. 17) housed in the selector handle and pivotally mounted thereon at 246, has an arm 247 with an indexing tab 248 on its upper side to engage in any of three indexing notches 249, 250, 251 in the upper bracket 238. Thus, the ammunition feeding trays are pivoted so that the right-hand tray is in operable position when the forward notch 249 is engaged, the left-hand tray is in operable position when the rearward notch 251 is engaged, and both trays are out of operable position when the intermediate notch 250 is engaged. The latch 245 is urged into the engaging position by a spring 252 interior of the selector handle and is released by squeezing a depending arm 253.

As the type of ammunition in one tray may have different ballistic characteristics than the ammunition in the other tray, means are provided for adjusting a gunsight responsive to the selection of a feed tray. The sight includes a forward bead 255 and a rear peep sight blade 256. Referring particularly to FIGS. 14 and 25, rear sight blade 256 is mounted for vertical sliding movement in a channel shaped bracket 254 fixed atop the receiver with the forward side of the bracket being open. A cam follower 257 on the sight blade engages in a cam slot 258 formed in a horizontal channel bracket 259 fixed on the connector bar 255 and abutting the front face of the vertical bracket 254, so as to raise the rear sight when the left tray is operative and lower the rear sight when the right tray is operative in accordance with the predetermined different ballistic characteristics of the two types of ammunition.

Referring to FIGS. 22-24 the rounds of ammunition 27 are interconnected by an exemplary disintegrating link 262, the details of which do not form a part of this invention except as the links cooperate with the gun and feeding means of this invention. The belts of ammunition of each store are fed up through the ammunition trays alongside the receiver and then laterally inward through side discharge openings 263 in each tray and through opposite side openings 265 in the upper portion of the receiver which define the feeding station 30 of the receiver. From the ammunition feeding station, the rounds of ammunition are stripped and chambered by the reciprocating bolt as will be described hereinafter. The links 262 continue upward through top openings 266 in the top of each ammunition feeding tray where they separate from the belt and fall from the gun.

Referring to FIGS. 2, -15, 25, 27 and 28, it may be seen that the ammunition feeding means 7 includes similar cam rollers or followers 270 which cooperate with similar elongate inclined cam means 271 formed on opposite sides of the bolt carrier body 32 to operate the feeding mechanism. Since the cam means and the feeding mechanism on opposite sides of the receiver are similar, similar reference numerals will be used for the corresponding parts of both.

The cam means 271 includes an enlarged elongate shallow cavity 398 in the side of the carrier body 32. The lower sidewall or edge of the cavity 398 forms a lower cam surface 400 starting at a forward shoulder 401 making the rear end of a short, horizontal forward cam surface 402 which is the highest level of the cam means. The forward portion 400a of the lower cam surface 400 slopes sharply downwardly from the forward cam surface 402 towards the rear of the bolt carrier body 32 to a low point 400a near the lower edge of the bolt carrier in about one-fourth the length of the longitudinal stroke of the bolt carrier. In a working embodiment of the invention the low point was reached in about 26 percent of the stroke.

The remaining, or rearward, portion 400b of the lower cam surface slopes gradually upwardly to a short, horizontal rear cam surface 404 at the rear of the bolt carrier, the surface 404 being at a level a little less than half of the vertical stroke of the cam follower 270. The rear cam surface 404 in effect forms a continuation of the cam surface 400 and is a further portion of the lower edge of the cavity 398.

An elongated cam ramp 406 is pivotally mounted in the cavity 398 on a pin 408 which is supported by the bolt carrier body 32, as may be seen from FIGS. 10 and 28. Note that the same pin 408 supports a ramp 406 on both sides of the carrier body.

Still referring to FIGS. 10 and 28, small recesses 4l2 are formed in the outer surface of the carrier body 32 surrounding the pivot pin 408. Within each recess 412 is positioned a coil spring 414'surrounding the pin 408. One end of each spring engages a wall of the recess 412 in the carrier body 32 and the other end of the spring fits within a recess 415 on the inner side of each ramp 406 to engage a ramp surface forming the edge of the recess 415. The springs 412 are oriented to urge the ramps 406 in a counterclockwise direction as viewed in FIGS. 13-15.

The spring bias could of course be provided by other arrangements, one other example (not shown) being the formation of a leaf spring integral with the ramp in its central portion. The leaf spring would be biased against a member supported on the bolt carrier.

With the ramp positioned as shown in FIGS. 14 and 15, the forward end 406a of the ramp 406 engages the forward end of an upper edge 410 of the cavity 398 and is spaced from the forward portion 400a of the lower cam surface so that a slot 417 is formed between the lower cam surface 400 and the lower edge of the ramp 406. The rear portion 406!) engages the rear portion 400b of the lower cam surface 400 so that the slot 417 is closed in that area as viewed in FIG. 14.

Since the rear end 406b of the ramp is engaging the rear portion 400b of the lower cam surface, the upper rear edge of the ramp 406 is spaced from the rear end of the upper edge 407 of the cavity 398 in the bolt carrier 32 so as to define a slot 416 between the upper edge 407 and the upper surface 406d of the ramp 406. As may be seen, the slot 416 tapers forwardly so that it is closed at its forward end. The size of the slots 417 and 416 at their largest points is sufficient to enable the rollers 270 to roll therein. It can be seen that the slots 417 and 416 form generally a loop shape around the ramp 406.

As the bolt carrier is reciprocated axially, the cam follower 270 is reciprocated vertically as moved by the cam means 271. In the process the rollers 270 pivot the ramp 406 to a second position as shown in FIG. 13 wherein the rear end 406b is spaced from the rear portion 400b of the lower cam surface so that the rear portion of the lower slot 417 is large enough to permit the rollers 270 to move therein. At the same time the rear portion of the upper slot 416 is closed. Also in this second position of the ramp 406, the forward portion 406a of the ramp is pivoted downwardly to engage the forward portion 4000 of the lower cam surface, the end of the ramp being adjacent the shoulder 401. Thus, the forward portion of the lower cam slot 417 is closed and the forward portion of the upper slot 416 is opened. Note that in this position the ramp is held against the urging ofthe springs 414.

The length of the bolt carrier body 32 is greater than the stroke of the bolt carrier so that the cam followers 270 remain on the cam means 271 throughout the stroke. Also, the stroke of the bolt carrier is slightly longer than the axial or longitudinal length of the ramp 406 so that the cam followers 280 cam be moved onto the forward cam surface 402 and the rear cam surface 404 can thus between the lower cam surface 400 and the upper cam surface 406!) on the ramp 406.

Referring to FIG. 25, as well as to FIGS. 22 and 23, each cam follower 270 is approximately centered at the feeding station 30 (see FIG. 2) and is rotatably mounted on a pawl carrier 272 by a horizontal axle 273 near the longitudinal center of the carrier. Each of the pawl carriers 272 is interposed between the bolt carrier body 32 and one of the ammunition feeding trays. The pawl carrier 272 reciprocates vertically toward and away from the feeding station in a rectangular opening 274 formed in the side of the receiver. Elongate tongues 275 on the forward and rear edge of the pawl carrier engage in corresponding vertical grooves 276 in the side of the receiver to guide the pawl carrier in its vertical reciprocation. A pair of similar feed pawls 277 are each pivotally mounted on the pawl carrier, one forward of the cam follower 270 and one rearward. The pawls 277 are spring biased outward to protrude through vertical slots 278 in the inboard sides 279 of the corresponding ammunition feeding trays and engage the rounds of ammunition contained in the tray. The pawls are free to pivot upwardly, but downward pivoting of the pawls is limited by the lower end of each pawl abutting the inner wall 280 of the pawl carrier.

A pair ofidentical inwardly extending, spring-loaded retaining pawls 283, only one of which is shown in FIG. 25, are pivotally mounted on a support 284 which is on the outboard side of the feeding tray, and are biased inward by springs 285 to engage the rounds. Downward pivoting of the retaining pawls is limited by abutment of their lower ends 286 (see FIG. 26) against the support 284.

While the overall operation of the gun will be subsequently described in greater detail, the operation of the feed mechanism by the bolt carrier will be described at this point. As may be gathered from the preceding description, the bolt carrier reciprocates axially during operation of the gun, part of this reciprocation occuring with the barrel reciprocation and part being relative to the barrel. This axial movement of the bolt carrier is utilized to vertically reciprocate the cam followers 270, which in turn operate the feed mechanism. Note that the movement of the cam follower is perpendicular to the movement of the bolt carrier.

Referring to FIGS. 29-33 the bolt carrier supporting the cam means 271 is shown in the various positions of axial reciprocation as occur during operation of the gun, and the cam followers 270 re shown in the corresponding positions of vertical reciprocation on a vertical line 418. Referring first to FIG. 29, the bolt carrier is shown in its rearwardmost position, this being comparable to the position of the gun as shown in FIG. 14, which is the open battery position of the gun. At that point, it can be seen that the cam follower 270 is resting on the forward cam surface 402. This is the highest position that the cam follower attains, thus the top of the feed stroke. The ram 406 is shown urged into its counterclockwise position by its biasing springs 414 (FIG. 28) such that the forward end of the lower cam slot 417 is open.

As the bolt carrier 32 commences its forward movement, indicated by the arrow 420 in FIG. 30, the cam follower 270 moves from the forward cam surface 402 into the cam slot 4l7 and onto the downwardly sloping forward portion 400a of the lower cam surface 400. Since the slope of the forward portion 400a of the lower cam surface 400 is quite steep, the cam follower 270 moves downwardly to the lowest point 400s of its stroke while the bolt carrier is moved forwardly only at the beginning portion of its forward stroke. Because of the speed of the bolt carrier, this downward movement of the follower occurs in a very short time interval; however, no ammunition is moved during the downward stroke and the only moving parts are relatively light in weight and are moving downwardly with the assistance of gravity. Consequently, this rapid acceleration can easily be attained.

Referring to FIGS. 25 as well as FIGS. 22 and 23, it may be seen that the parts actually moved by the cam follower in its downward stroke are the pawl carriers 272 supporting the feed pawls 277. During the downward stroke. the pawls are cammed inwardly by a round of ammunition 27c as they pass. At the bottom of their stroke, the feed pawls 277 are beneath the round of ammunition 27c to be engaged because the pawl springs 282 bias the pawls outwardly, as shown in FIG. 23.

As the bolt carrier continues its forward stroke, the cam follower 270, rolling in contact with the rear portion 400!) of the lower cam surface 400, is raised from the position shown in FIG. 30 to that of FIG. 31 at a gradual rate due to the gradual upward slope of the cam surface 400b. As the bolt carrier moves forwardly the cam follower 270 moves upwardly, it engages the rear portion of the lower edge 4060 of the ramp 406. Since the pin 408 has moved forward of the follower 270, the follower pivots the ramp in a clockwise direction against the urging of its springs into the position shown in FIG. 3]. This enables the cam follower 270 to move onto the rear cam surface 404 as the bolt carrier completes its forward stroke as shown in FIG. 32, and 2, which is the in battery position for the gun.

In this position the ramp 406 carried by the bolt carrier has been moved forwardly such that it no longer engages the cam follower 270, and hence the ramp snaps quickly in a counterclockwise direction due to the urging of its spring 414 (FIG. 28) to a position wherein its rear portion 406b once again engages the lower cam surface 400b and its forward portion 406a is once again spaced from the forward, lower cam surface 4000. The cam follower 270 has at this point moved upwardly approximately 40 percent of its upward stroke, with its feed pawls 277 fitting the belt of ammunition, as may be visualized from FIGS. 22 and 23. As the belt of ammunition is raised, the retaining pawls 283 pivot upwardly out of the way of the round of ammunition.

With the cam follower and the bolt carrier, as shown in FIG. 32, the ramp is positioned to enable the cam follower to move into the cam slot 4I6 and onto the upper cam surface 406d forming the upper edge of the ramp as the bolt carrier is moved rearwardly on its return stroke, thus continuing the upward movement ofthe cam follower. As the bolt carrier moves rearwardly, as shown by the arrow 422 in FIG. 33, causing the cam follower to move upwardly from the position in FIG. 32 to that of FIG. 33, the pivot pin 408 moves to the rear of the follower 270 so that the ramp is once more pivoted in a clockwise direction to the position shown in FIG. 33, wherein the forward end 4060 of the ramp engages the forward portion 400a of the lower cam surface 400. Due to the shoulder 40] receiving the ramp end 406, the forward cam surface 402 in effect forms a continuation of the leading edge of the upper cam surface 406d so that the cam follower can move smoothly onto the forward cam surface as the bolt carrier contemplates its return or rearward stroke, returning to the position shown in FIG. 29, completing its upward stroke.

As soon as the cam follower rolls onto the forward cam surface 402, the ramp once more immediately snaps counterclockwise to the position shown in FIG. 29. Thus, it can be seen that the pivoting movement of the ramp enables the cam follower to move in a loop and that the ramp is pivoted and then pivots back twice during the complete cycle of the bolt carrier and cycle of the cam follower.

With the cam follower in its uppermost position, the retaining pawls 283 are in position to snap outwardly to a position beneath the raised round 27!) as may be seen in FIG. 23, thereby retaining the belt of ammunition in position while the feed pawls 277 reciprocate downwardly to engage the next round during the next cycle of the feed mechanism.

In view of the foregoing operation of the feed mechanism, it can be appreciated that an advantage of the arrangement is that an upward stroke of the feed mechanism occurs during about seven-eighths of the bolt carrier cycle, while the return stroke occurs during about one-eighth of the entire cycle. As a result, the time available for moving the relatively heavy belt of ammunition is maximized. Thus, the acceleration forces which must be developed and applied to the belt of ammunition are kept at a minimum. This decreases the likelihood of separations occurring in the belt of ammunition and maximizes the speed at which the gun can be operated to the extent that ammunition feed rate is one of the limiting factors in determining the speed of the gun.

An upwardly and inwardly extending plate spring 288 guides the upper round 27a laterally to the feeding station 30, from where it is stripped, chambered and fired. One end of the guide spring 288 is affixed to a rod 290 extending between a pair of spaced guide arms 291 (see also FIG. 26). The other end is attached to the upper end of the ammunition tray; and the center of the plate is bent around a rod 292 which is fixed to the support 284 and on which the guide arms 29! are pivotally mounted.

The side opening 263 in each tray has a rear portion 302 which is narrower than the diameter of the rear part of the round 27 and a forward portion 300 which is wider than the widest part of the round 27. The opening 263 is contiguous with an opening 301 in the forward wall of the tray. The raised round 27 is held in the tray since it can not pass completely through the narrow rear portion 302 of the opening. However, the round 27 does protrude far enough through the side opening 263 of the tray, under the urging of spring plate 288, that if the tray is in operating position, the bolt 28 engages the rear of the round as the bolt comes forward. The bolt 28 strips the round 27 out of the links 262 and rams the round forward and inward through the forward portion 300 of the side opening 262 and the opening 301 into the chamber of the barrel.

The empty links 262 are guided up out of the opening 266 in the top of the ammunition trays by forwardly and rearwardly extending tabs 293 on the links (see FIG. 24) which engage in vertical guide grooves 294 in the upper end of the space guide arms 291.

A positioning stop 295 engages the round 27a at the feeding station 30 to positively limit upward movement of the round and fix it at the feeding station. This stop is pivotally mounted about a horizontal transverse axis on the upper plate 296 of the ammunition tray so that as the round moves forward to the chamber, the stop is cammed forward out of the way by the cartridge case. A spring 297 returns the stop to its operative position. The forward end of the round is guided into the chamber by a ramp guide 299 on the forward end of the ammunition tray and tapered surfaces 298 of the locking teeth 16] adjacent opposite sides of the barrel extension (see FIG. 21).

When an ammunition tray is pivoted to the inoperative position, as for example the left-hand tray in FIGS. 22 and 23, the feed pawls will continue to reciprocate as the bolt carrier reciprocates, but the rounds of ammunition in the tray are far enough outboard of the feed pawls that the pawls do not engage the rounds, and no ammunition is fed from that tray. The top round is held in the tray since it can not pass through the rear portion 302 of the side opening 263 far enough to be engaged by the bolt. Since the retaining pawls are part of the tray they remain effective to support the rounds in the tray so it is ready to feed ammunition when pivoted to the operative position.

The outboard sideplate 303 of each ammunition tray is designated to be opened for access to the interior of the tray. The sideplate is pivotally attached to the forward vertical mounting rod 219 by a bracket 304 affixed to the forward end of the sideplate and having ears 305 through which the mounting rod is inserted. The rear edge 306 of the sideplate extends rearward of the ammunition feeding tray so that it may be gripped to pivot the sideplate to the open position.

With the sideplate open, the ammunition in the tray may be removed by pulling upwardly on a U-shaped release handle 307. The release handle 307 is an extension of a U-shaped connector 309, the ends of which are attached around the guide plate support rod 290. As the release handle 307 is pulled, the guide arms 291 pivot outwardly to pull the guide plate spring 288 away from the rounds of ammunition as shown in phantom in FIG. 22. The release handle is also connected to the retaining pawls 283 by wires 308 attached to the connector 309. The wires 308 pull the retaining pawls outwardly from under the rounds of ammunition when the release handle 307 is pulled. The rounds can then be pulled downward out of the tray to unload the gun.

The operation of the gun can best be understood by following through a complete firing cycle beginning with the gun in the firing position shown in FIG. 2. When the round is fired, the barrel 5 recoils rearwardly in the receiver 6. The recoil piston 73 which is affixed to the barrel moves rearwardly in the stationary recoil cylinder 70 as the barrel recoils, thereby driving the accelerator piston 93 rearwardly. Since the crosssectional area of the recoil piston head 75 is larger than that of the accelerator piston head 95, e.g. by a ratio of three to two, the accelerator piston moves rearward faster than the barrel and recoil piston.

The rear end of the accelerator piston rear extension 107 engages the forward end of the bolt carrier body 32 to drive the bolt carrier rearward at an accelerated rate relative to the barrel. When the barrel has completed an initial part of its recoil, e.g. one-half inch, the accelerator piston 93 has moved rearward a sufficient distance, e.g., three-quarters of an inch, to bottom out in the recoil cylinder 70, as shown in FIG. 7. By that time the accelerator piston has imparted sufficient momentum to the bolt carrier 29 to send the bolt carrier and bolt 28 rapidly to the rear of the receiver. Also by then, the forward face of the recoil piston head 75 has passed the forward edge of the wedge-shaped throttling groove H0 in the cylinder wall, so that the groove becomes effective to pass fluid around the recoil piston head. The throttling groove decreases in cross-sectional area in the rearward direction, so that the quantity of fluid which passes through it decreases at a programmed rate as the recoil piston moves rearward, thereby cooperating with the recoil spring 98 to buffer the recoil force of the barrel and bring the barrel and recoil piston to a stop with the recoil piston slightly spaced from the accelerator piston forward extension 101, and the barrel extension 48 slightly spaced from a shoulder 310 on the receiver, as shown in FIG. 8.

As is shown in FIG. 7, during the first part of the recoil cycle, the bolt 28 is locked to the barrel by the locking teeth 160, 161 while the bolt carrier moves rearward at a faster rate than the bolt and barrel and the bolt cam follower pin I62 moves through the rearward axial portion of the bolt carrier sleeve cam slots 163. By the time the bolt carrier has traveled rearwardly with respect to the barrel and bolt sufficiently so that the cam follower 162 of the bolt enters the central portion of the cam slots 163 to rotate the bolt to the unlocked or aligned position, the residual pressure in the barrel chamber has been somewhat dissipated, thereby reducing the friction between the teeth I60, 161 of the bolt and barrel. After the bolt is in the aligned or unlocked position a further short dwell period occurs while the cam pin 162 moves through the forward portion of the sleeve cam slots 163. As the cam pin engages the forward end of the cam slots, the bolt moves rearward with respect to the barrel and the extracting claw 168 which is engaged with the lip of the expended cartridge, extracts the cartridge from the chamber and carries it rearward with the bolt. Extraction of the cartridge from the chamber occurs between the positions illustrated in FIGS. 7 and 8 so that the barrel is still recoiling, even though it is in its deceleration phase. Thus, the relative velocity between the bolt and the barrel as the cartridge is removed is less than if the barrel were stopped, so that removal of the cartridge is eased.

When the bolt 28 begins to move rearward away from the barrel, the bolt carrier sleeve 31 is rearward with respect to the bolt, and the crevice pin 165 is urged upward by the spring 164 into the notch 166. After the bolt leaves the barrel, the ramping pin 167 holds the crevice pin engaged in the notch to keep the bolt in the aligned position until its locking teeth 160 are again engaged in those 161 of the barrel.

Referring now to FIG. 9, as the bolt and bolt carrier continue rearward with the cartridge case, the recoil spring 98 and accelerator spring urge the accelerator piston 93, recoil piston 73 and barrel 5 forward in counterrecoil to the position shown in FIG. 2. During the initial part of the counterrecoil cycle of the barrel, fluid passes the recoil piston head 75 both through the wedge-shaped throttling groove and 

1. An automatic gun including (a) a receiver having an ammunition feeding station therein, (b) a barrel, (c) a bolt carrier adapted to reciprocate axially in said receiver past the feeding station, (d) cam means extending along the exterior of the bolt carrier, and (e) ammunition feeding means attached to the receiver having a cam follower which is reciprocated by the cam means on the bolt carrier for feeding ammunition to the feeding station, the improvement wherein said cam means comprises: a lower cam surface for guiding said follower while said carrier is moving in one direction; an upper cam surface in communication with said lower cam surface for guiding said follower while said carrier is moving in the opposite direction; the cam surfaces being oriented such that the cam follower is raised an initial amount while engaging a substantial portion of the lower cam surface, and then raised the rest of its stroke while engaging the upper cam surface; the forward portion of the lower cam surface slopes sharply downwardly toward the rear such that the cam follower is quickly lowered when in contact with said forward portion as the carrier is moving forwardly, and the remaining portion of said lower cam surface slopes gradually upwardly so that the follower is raised when in contact with this remaining portion as the carrier moves forwardly; and said upper cam surface slopes gradually upwardly in a forwardly direction so that the follower is raised when in contact with said upper cam surface as the carrier is moved rearwardly.
 2. An automatic gun including (a) a receiver having an ammunition feeding station therein, (b) a barrel, (c) a bolt carrier adapted to reciprocate axially in said receiver past the feeding station, (d) cam means extending along the exterior of the bolt carrier, and (e) ammunition feeding means attached to the receiver having a cam follower which is reciprocated by the cam means on the bolt carrier for feeding ammunition to the feeding station, the improvement wherein said cam means comprises: a lower cam surface for guiding said follower while said carrier is moving in one direction; an upper cam surface in communication with said lower cam surface for guiding said follower while said carrier is moving in the opposite direction; the cam surfaces being oriented such that the cam follower is raised an initial amount while engaging a substantial portion of the lower cam surface, and then raised the rest of its stroke while engaging the upper cam surface; a forward cam surface forming an extension of the forward portion of the lower cam surface; a rear cam surface forming an extension of the rear portion of the lower cam surface; the stroke of said carrier being such that when the carrier is in its rearwardmost position, the cam follower rests on said forward cam surface, and when the carrier is in its forwardmost position, the cam follower rests on said rear cam surface; pivotal means for enabling the follower to be moved in sequence from said forward cam surface onto the lower cam surface, onto the rear cam surface, onto the upper cam surface, and back to the forward cam surface, while said carrier is reciprocated one cycle; said upper cam surface and said pivotal means comprise a ramp mounted on said carrier adjacent said lower cam surface and between said front and rear cam surfaces, the upper surface of the ramp forming said upper cam surface, the ramp being pivotal from a first position wherein its forward end is spaced upwardly from said forward cam surface sufficiently to permit the follower to move from said forward cam surface onto said lower cam surface while the rear end of the Ramp forms an extension of said rear cam surface to permit the follower to move from said rear cam surface onto said upper cam surface, to a second position wherein the forward end of the ramp leads onto said forward cam surface while the ramp rear end is spaced sufficiently from said rear cam surface to permit the follower to move from the lower cam surface onto said rear cam surface; and means for biasing said ramp into its first position, the strength of the biasing means being such that it is overcome by the follower as it is moved by the carrier.
 3. An automatic gun comprising: reciprocating means for driving a round of ammunition into the gun barrel including cam means formed on said driving means; and ammunition feed means for feeding a round of ammunition into position wherein it can be engaged by said driving means including a cam follower engaging said cam means to be reciprocated by said cam means in a direction generally perpendicular to the direction the driving means is reciprocated; said cam means including cam surfaces for moving said follower through one stroke of its cycle during only a portion of one stroke of the cycle of said driving means, and for moving said follower through the other stroke of its cycle during the remainder of said one stroke of the driving means and during the other stroke of the driving means cycle.
 4. An automatic gun comprising: reciprocating means for driving a round of ammunition into the gun barrel including cam means formed on said driving means; and ammunition feed means for feeding a round of ammunition into position wherein it can be engaged by said driving means including a cam follower engaging said cam means to be reciprocated by said cam means in a direction generally perpendicular to the direction the driving means is reciprocated; said cam means including cam slot means arranged generally in the form of a loop and including means for directing the cam follower to move in the proper direction in said loop; and said means for directing the cam follower is a pivotally mounted elongated ramp forming the center of the loop-shaped cam slot means.
 5. In a recoil-operated automatic gun including (a) a receiver having an ammunition feeding station therein, (b) a barrel mounted for reciprocal axial movement, (c) a bolt disposed in axial alignment with the barrel, (d) a bolt carrier adapted to reciprocate axially in said receiver past the feeding station, (e) cam means extending along the exterior of the bolt carrier, (f) ammunition feeding means attached to the receiver, having a cam follower which cooperates with the cam means on the bolt carrier for feeding ammunition to the feeding station, and (g) recoil means coupled between the barrel and bolt carrier to accelerate the bolt carrier in recoil relative to the barrel, the improvement wherein said cam means comprises: a lower cam surface extending along the outer surface of the bolt carrier, the forward portion of the lower cam surface sloping sharply downwardly towards the rear, the remaining portion of the lower surface sloping gradually upwardly toward the rear; a forward cam surface forming an extension of the forward portion of the lower cam surface; a rear cam surface forming an extension of the rear portion of the lower cam surface; the stroke of said bolt carrier being such that when the carrier is in its open battery position, the cam follower rests on said follower forward cam surface, and when the carrier is in its inbattery position, the cam follower rests on said rear cam surface; a ramp pivotally mounted on said bolt carrier adjacent said lower cam surface between said front and rear cam surfaces, the upper surface of the ramp forming an upper cam surface for the cam follower which slopes gradually upwardly from its rear ends towards its forward end, the ramp having a first position wherein its forward end is spaced upwardly from said forward cam surface sufficiently to permit the fOllower to move from said forward cam surface onto said lower cam surface and wherein the rear end of the ramp forms an extension of said rear cam surface to permit the follower to move from the rear cam surface onto said upper cam surface, and the ramp having a second position wherein the forward end of the ramp leads onto said forward cam surface and wherein the ramp rear end is spaced sufficiently from said rear cam surface to permit the follower to move from the lower cam surface onto said rear cam surface; and means for biasing said ramp into its first position, the strength of the biasing means being such that it may be overcome by the follower being moved by the carrier.
 6. The gun of claim 5 wherein the forward portion of said lower cam surface is less than one-half of the entire lower cam surface whereby the cam follower is lowered its full amount in less than one-half of the rearward stroke of the bolt carrier while the cam follower is raised during the remainder of the rearward stroke and during the forward stroke of the carrier.
 7. The gun of claim 5 wherein the forward portion of said lower cam surface is formed such that the cam follower is lowered its full amount in about one-quarter of the distance of the bolt carrier moves on its rearward stroke.
 8. The gun of claim 6 wherein said biasing means includes a coil spring mounted on said bolt carrier in a manner to bias the ramp into its first position.
 9. The gun of claim 5 wherein said bolt carrier is formed with an enlarged elongated cavity in its side wall and said forward, lower, and rear cam surfaces form the lower edge of the cavity, and said ramp is positioned within said cavity. 